The present invention relates to an information recording medium where key information is recorded in a medium disk-shaped, tape-shaped or card-shaped, a reproducing method and a truth judging method for the information recording medium capable of preventing illegal usage of the information recorded in the medium by reproducing of the key information, and a recording/reproducing apparatus for recording, and reproducing the information recording medium provided with the key information.
An optical disk, capable of recording mass information with a portable size, is examined for practical use as a recording media core of the rapidly developing multi-media. The optical disk is considered important for managing of the recorded information such as prevention of illegal usage of the information, because the optical disk is capable of recording mass information.
The applicant of the present application proposes a copy preventing method of forming artificial defects in the optical disk by Japanese Patent Application Laid-Open No. 5-26676 (1993) with an eye to preventing the illegal use of the information. The method judges it genuine that both the addresses agree through comparing the respective addresses of an address registration part and a PDL area in the optical disk use with the address registration part with artificially defected addresses recorded on it and the PDL (Primary Defect List) for recording the artificially defected addresses detected by physical format being formed in the optical disk. The medium truth can be judged due to disagreement between both the addresses, because the illegal copy does not allow the PDL area to be copied as the PDL area is formed in non-access area where users cannot access in a normal method. But the information may be used illegally when the user manages to access to the PDL, area of the optical disk by some methods.
Also, the applicant proposes a method of protecting information with the use of media identification codes by Japanese Patent Application Laid-Open No. 5-257816 (1993). The publication describes a method of producing media inherent keys in accordance with the media identification codes inherent to the optical disk to encode, record the information to be recorded with the use of the media inherent keys, and a method of reproducing the encoded information recorded to decode with the use of the media inherent keys. But the methods could not realize the prevention of the illegal use without description of a method of forming medium identification codes.
To establish a method of preventing the illegal usage of such information, the applicant proposes a method of forming medium identification codes by U.S. patent application Ser. No. 08/620,08. This method records the medium identification code of a predetermined hit number irreversibly, namely, unrewritably on the optical disk. The truth or false judgment as to whether or not an optical disk to be used is a genuine product is effected by conduction of an erasing operation on an area where the medium identification codes are recorded, the optical disk proves to be genuine when it is not erased, and the optical disk is prohibited from using the information as an illegal copy when it is erased.
The proposition can prevent the illegal usage of the information. But the reproducing signals of the medium identification code recorded irreversibly may not be recognized as medium identification signals because of smaller signal amplitude.
Also, when reproducing such an optical disk, a special reproduction processing, namely, recording operation and reproducing operation after the erasing operation is effected on the specified area where the medium identification codes are recorded. Thus, a program instructing what type of reproduction processing in which area should be effected is recorded in the optical disk. The data of the program is sent to a computer connected with the recording/reproducing apparatus of the optical disk. The computer gives to the recording/reproducing apparatus instructions for special reproduction processing in accordance with the given data to judge whether or not the optical disk is true or false as described above.
In the above described processing, the data on the medium truth judgment using the medium identification code can analyze data on the medium truth judgment with some operation of the user, because the data are transferred between recording/reproducing apparatus and the computer. There has been a problem where illegal copy can be used by the analysis and information copied illegally from the genuine product can be used.